The neural retina is necessary for regeneration of the lens in the newt. The proposed research will investigate the effect of the neural retina and retinal extracts on regeneration of the newt lens in organ culture. These experiments will specifically address the questions of whether the retina enhances lens regeneration by acting to promote mitosis, allowing iris epithelial cells to progress through a requisite number of mitoses prior to expression of their tendency to form lens, and whether the effect of the retina in culture can be duplicated by retinal homogenates, retinal extracts or retina-cell conditioned culture medium. The results of these experiments will help define the nature of the retinal effect in regeneration of a lens and the nature of the factor(s) responsible for it, yielding information important in our understanding of cell transdifferentiation and the neural influences on that process. To this end, 11-day-old lens regenerates will be explanted to organ culture medium enriched with neural retinal homogenates or extracts of the retina, or cultured directly on top of neural retina. Mitosis and DNA synthesis will be inhibited by treatment of the cultures with hydroxyurea, thymidine, colchicine, cytochalasin B or D, and the effects of this treatment on the ability of the neural retina to enhance regeneration to stages producing gamma crystallin protein will be assessed. The influence of retina and its extracts on DNA synthesis and mitosis will be monitored and compared to the effects of other control tissues and extracts. Regeneration of the lens is a clear example of transdifferentiation or metaplasia which results in the production of a second, normal cell type from the original one. Thus, it is important to understand how the differentiated state of these cells is controlled. Since factors produced by the retina in humans after ocular injury may influence the ocular lens, it is important to understand retina-lens interactions in this model system which can be more easily manipulated and controlled.